geom

https://github.com/tmpvar/vec2.js

https://github.com/jnordberg/geometry.js

https://github.com/okcupid/node-geom2d/

https://github.com/STRd6/matrix.js

http://paulbourke.net/geometry

http://www.codeproject.com/Articles/15573/2D-Polygon-Collision-Detection

http://softsurfer.com/algorithm_archive.htm

https://github.com/polygonal/core

https://en.wikipedia.org/wiki/Machine_epsilon